This is a simple x86 assembly program that solves the puzzle Reverse Binary Numbers as seen on Open Kattis. It compiles to a statically linked ELF32 executable (Linux) for the Intel 80386 architecture. Since ELF32 is forward compatible, it will compile and run on x86-64 Linux distributions as well.
Basically, the program reads a decimal integer N, where 1≤_N_≤1,000,000,000. It reverses the integer's binary representation, and writes back the result in its decimal form. For example, 13 ("1101") returns 11 ("1011") and 47 ("101111") returns 61 ("111101").
Note that Kattis doesn't permit solutions in assembly language, so this project can't really help you to cheat. Anyone who can read and understand this code could surely also have solved the problem in another language without assistance.
Details about the implementation can be found in the source code.
Install the basic build tools (from which you need make and ld) and
nasm on your Linux machine. Then, in the project directory, run
make
- An instruction on how to create small executables. The machine code version of the program is 86 bytes long, but the executable is around 396 bytes. There are ways to create ELF files with less overhead than that by handcrafting them.
- An example of completely optimized code. I'm sure there's room for more optimizations. Readability was taken into account, and I only removed some obvious redundancies.
- An example of how to write robust code. There are no checks in place to verify the validity of the input.
- An example of how to do anything in real life. I wrote this just for fun. There are definitely uses for assembly language, but this is not one of them. Play around with the project as much as you want, but remember that you should rarely have to consider writing a program purely in assembly language nowadays. When you do, it'll most likely be for an embedded system, and not for server/desktop/laptop.